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Tue, 20 May 2025 19:47:17 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFzkHF4ER+v9r//dGWI45mzF35nZdjti9WpLsYuT60Xr9ICzKlggdIDgLPRs9dM7JzLT2yOBw== X-Received: by 2002:aa7:8e8a:0:b0:742:b3a6:db09 with SMTP id d2e1a72fcca58-742b3a6dbdbmr19583136b3a.16.1747795636622; Tue, 20 May 2025 19:47:16 -0700 (PDT) Received: from [192.168.68.51] ([180.233.125.65]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-742a970d1b2sm8941786b3a.66.2025.05.20.19.46.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 May 2025 19:47:15 -0700 (PDT) Message-ID: <498765f6-c20e-48f2-98e4-4134bfe150a3@redhat.com> Date: Wed, 21 May 2025 12:46:55 +1000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 15/17] KVM: Introduce the KVM capability KVM_CAP_GMEM_SHARED_MEM To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org Cc: pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com References: <20250513163438.3942405-1-tabba@google.com> <20250513163438.3942405-16-tabba@google.com> From: Gavin Shan In-Reply-To: <20250513163438.3942405-16-tabba@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CLKGBSf64AfuO-EKs5fEK38VuT-8MzpVigrFjRoNEME_1747795637 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: zwekm5q5qzo4ghn6fpmi3gfixfikefpc X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8798D18000A X-HE-Tag: 1747795644-73865 X-HE-Meta: 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 eTrZ753x 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Fuad, On 5/14/25 2:34 AM, Fuad Tabba wrote: > This patch introduces the KVM capability KVM_CAP_GMEM_SHARED_MEM, which > indicates that guest_memfd supports shared memory (when enabled by the > flag). This support is limited to certain VM types, determined per > architecture. > > This patch also updates the KVM documentation with details on the new > capability, flag, and other information about support for shared memory > in guest_memfd. > > Signed-off-by: Fuad Tabba > --- > Documentation/virt/kvm/api.rst | 18 ++++++++++++++++++ > include/uapi/linux/kvm.h | 1 + > virt/kvm/kvm_main.c | 4 ++++ > 3 files changed, 23 insertions(+) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 47c7c3f92314..86f74ce7f12a 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -6390,6 +6390,24 @@ most one mapping per page, i.e. binding multiple memory regions to a single > guest_memfd range is not allowed (any number of memory regions can be bound to > a single guest_memfd file, but the bound ranges must not overlap). > > +When the capability KVM_CAP_GMEM_SHARED_MEM is supported, the 'flags' field > +supports GUEST_MEMFD_FLAG_SUPPORT_SHARED. Setting this flag on guest_memfd > +creation enables mmap() and faulting of guest_memfd memory to host userspace. > + > +When the KVM MMU performs a PFN lookup to service a guest fault and the backing > +guest_memfd has the GUEST_MEMFD_FLAG_SUPPORT_SHARED set, then the fault will > +always be consumed from guest_memfd, regardless of whether it is a shared or a > +private fault. > + > +For these memslots, userspace_addr is checked to be the mmap()-ed view of the > +same range specified using gmem.pgoff. Other accesses by KVM, e.g., instruction > +emulation, go via slot->userspace_addr. The slot->userspace_addr field can be > +set to 0 to skip this check, which indicates that KVM would not access memory > +belonging to the slot via its userspace_addr. > + This paragraph needs to be removed if PATCH[08/17] is going to be dropped. [PATCH v9 08/17] KVM: guest_memfd: Check that userspace_addr and fd+offset refer to same range > +The use of GUEST_MEMFD_FLAG_SUPPORT_SHARED will not be allowed for CoCo VMs. > +This is validated when the guest_memfd instance is bound to the VM. > + > See KVM_SET_USER_MEMORY_REGION2 for additional details. > [...] Thanks, Gavin